| Macaca rhesus(Macaca mulatto) as an endangered species and important experimental animals is was widely distributed in China. However, there was a sharp decline in the number and serious habitat fragmentation due to the impact of human activities. Major histocompatibility complex (MHC) genes are specific to vertebrates and main involved immune response as one of the important multi-gene family. MHC class Ⅱ genes encoded antigen binding region exhibits a high level of polymorphism, cause of mainly involved in recognition of outside pathogens. Thanks to this, MHC genes is considered the best marker of vertebrate adaptive mechanism. Currently, MHC gene polymorphism and evolutionary mechanisms become a conservation biology research focus. This study used combines by polymerase chain reaction-single strand conformation polymorphism analysis (PCR-SSCP) and clone-sequencing techniques to analysis polymorphism of 142 individuals MHC-DQB1 gene in Sichuan six wild populations, and combined with the previous microsatellite data of the Sichuan region macaque to discussed adaptive mechanisms. Our study will provide the basis for genetic resources conservation strategies of the macaques on the one hand and also play a guiding role for the using of captivity monkeys on the other hand. The main results are as follows:(1) In this study, we detected 27 different Mamu-DQB1 alleles from 142 wild macaques, frequency of three alleles is exceeded 10%, they are Mamu-DQB1 * 0614,*1503 and *1703, and Mamu-DQB1*0614 is the highest frequency of allele among them. It’s indicating they are dominant allele in Sichuan rhesus monkeys, and may be related some common pathogens. Alignment of the sequences of 27 Mamu-DQB1 exon 2 indicated 92 nucleotide variable sites and 43 amino acid variable sites. From this results, indicating that Mamu-DQB1 exon 2 of Sichuan macaques have a high level of genetic polymorphism.(2) 27 Mamu-DQBl alleles belong to six DQB lineages of macaque(Mamu-DQB1* 06, * 15,* 16,* 17,* 18,* 24), which are all previously reported. From phylogenetic tree, indicated MHC-DQB1 alleles of rhesus and cynomolgus monkeys gather though lineages, not species or samples. Comparing the two species alleles found 14 identical shared alleles, there are 11 alleles in this study, suggesting a high level of trans-species polymorphism exit between rhesus and cynomolgus monkeys. No matter what, historic balance selection play an important role to remain ancestral alleles. However, analysis of selective pressure of Mamu-DQB1 exon 2 indicated nonsynonymous substitutions (dn) was higher than synonymous substitutions (ds) for the antigen binding sites (ABS) and non-antigen binding sites (Non-ABS), indicating that Mamu-DQB1 is subject to positive selection, but it’s not significant using Z-test. Indicating force of balancing selection is relatively weak to this sites.(3) Analysis of population genetic differentiation revealed value of gene flow among six populations is more than one, but distinct differentiation already happen among six populations, and heishui populations have maximum differentiation and minimum gene exchange with other populations. We speculate that these populations influence by genetic drift.(4) Analysis of population structure patterns showed pairwise Fst value of Mamu-DQB1 are not always more than microsatellite, that selection pressure is different for six populations. In a word, balancing selection on Mamu-DQBl is not strong enough to counteract drift that results from population fragmentation, isolation and so on. |
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